Method of channel allocation for a mobile terminal moving in a cellular communication network

ABSTRACT

The present invention proposes a method of channel allocation for a mobile terminal (MS) moving in a cellular communication network (NW), said method comprising the steps of: detecting (S 21 ) the speed of said mobile terminal (MS) moving in said network, and dependent on said detected speed (S 23 , S 25 ), allocating (S 24 , S 26 , S 27 ) a channel of a specific type to said mobile terminal (MS). Accordingly, with the present invention implemented, delays in neighbor cell SCH decoding and signal level measurement are significantly reduced and may thus no longer result in incomplete data for inter-cell handover decision or even unsuccessfull handovers. Hence, communication network performance in particular in connection with handovers in a cellular network layout is improved. The present invention also concerns an accordingly adapted device for channel allocation.

This application is a 371 of PCT/EP01/05519, filed on May 15, 2001.

FIELD OF THE INVENTION

The present invention relates to a method of channel allocation for amobile terminal moving in a cellular communication network.

BACKGROUND OF THE INVENTION

Cellular communication networks such as the GSM network system havewidely spread in recent years with the increase of the demand for mobilecommunication.

FIG. 1 shows a rough outline of a part of a cellular communicationnetwork. Generally, the network area served by the network is composedof individual cells C1, C2, C3 . . . , and/or c1, . . . c7. Each cell inturn is served by a respective base station BS or base transceiverstation BTS (not shown in every cell). The coverage area of such a basestation BS is defined by the cell radius R and/or r. The coverage areaand cell radius are adjustable by the transmit power used by thetransmitter of the base station BTS.

Thus, dependent on the transmit power of the BTS used, the network maybe composed of so-called macrocells meaning a cell covering a large area(with a cell radius R of for example up to 30 km, or even more. Forexample, GSM standard allows cells of radius 35 km, while with specialwell-known cell extension techniques, the radius may be extended—inareas with prevailing radio propagation condition which allow this—up to120 km). Examples of such macrocells are illustrated in bold (solid anddashed) lines in FIG. 1 and labeled C1, C2, C3, respectively. On theother hand, a low set transmit power leads to a cellular networkcomposed of microcells meaning a cell covering a small area only, e.g.cells c1 to c7 in FIG. 1. (Note that in microcell network layouts thenumber of base stations per area—compared to macrocell layouts—needs tobe increased so that there do not arise gaps between the coverage areasof the microcells.) Although typically microcells have a cell radius rnot exceeding 500 m, this is not limiting for the present invention.Rather, a microcell in the present specification is to be understood asa cell covering a small area such that the coverage area of plural smallcells (c1, . . . , c4) is comprised in the coverage area of a large cell(C1), as it is illustrated by way of example in FIG. 1. Also, asillustrated in FIG. 1, cellular networks may adopt a cellular structurein which a macrocell layout is overlaid to a microcell layout.Nevertheless, a microcell layout may be provided for without an overlaidmacrocell layout (and vice versa). Microcell layouts are preferably usedin “hot spots” of the network where a high demand for mobilecommunication services is expected to occur such as in shopping malls,airports, etc.

A mobile terminal located in such a cellular communication networkcommunicates with and/or via the network via an air interface betweenthe terminal MS and the base station BS in a manner known as such ingeneral and as for example set out in various GSM specifications, e.g.based on TDMA and/or CDMA etc.

As the terminal MS is mobile it may move at different speeds within thecellular network area. Also, when moving, it may cross one or moreborders of the cells shown in FIG. 1. Upon crossing a cell border, themobile terminal in most cases may require to be handed over to a newserving base station BS of the new cell to which it has moved. Such ahandover is defined as a feature involving a change of physicalchannels, radio channels and/or terrestrial channels, involved in a callwhile maintaining a call. (A call being a logical association to/fromthe mobile terminal from/to a switch.) This change of channels might berequired as caused by the movement of an active terminal (crossing acell boundary) or caused by spectrum, user profile, capacity or networkmanagement issues.

Data exchange between the base station and the mobile station via theair interface (sometimes referred to as U_(m) interface) according toGSM adopts, e.g. a time divisional multiple access scheme TDMA.According to TDMA, data are transmitted in units of bursts duringconsecutive time slots TS. Eight time slots according to GSM form oneframe. One frame according to GSM has a duration of 4.615 ms. It is,however, to be noted that the present specification refers to GSMspecific features only for explanatory purposes and other TDMA methods(for example adopting another number of time slots per frame, or anothertime duration per frame) may likewise be used in connection with thepresent invention. For example, the present invention as to be describedlater is easily applicable to the American IS-54 digital cellular systemadopting a TDMA scheme with 6 time slots per frame and a frame durationof 40 ms, or even to the Japanese digital cellular system having a 3channel TDMA multiple access scheme (full rate).

With regard to the GSM system again, individual frames are grouped in tomultiframes. Dependent on the type of signaling transmitted in themultiframes, two types of multiframes can be distinguished:

1) for traffic channels carrying/transmitting (mainly) user data, 26frames form a 26-multiframe (duration 120 ms), while

2) for signaling channels carrying/transmitting (only) control signalinginformation, 51 frames form a 51-multiframe (duration 235.38 ms).

Furthermore, 26*51 frames make up one superframe (duration 6.12 s),while 2048 times a superframe constitutes a hyperframe.

FIG. 3 illustrates an example of a 26-multiframe for a traffic channel.The 26 frames are numbered from #0 to #25. In the first 12 frames (#0 to#11) user data traffic is carried, frame #12 carries the SACCH (slowassociated control channel, an inband control channel assigned to thetraffic channel TCH or the slow dedicated control channel SDCCH). Frames#13 to 24 carry again user data traffic, and frame #25 is an idle framewhich is not used for transmission.

Rather, the idle frame is required to be reserved for terminals fordecoding SCH (synchronization channel) data transmitted in a51-multiframe from the base station to the mobile terminal.

More precisely, in GSM and/or GSM/EDGE networks (EDGE=Enhanced Daterates for GSM Evolution, GSM=Global System for Mobile communications),as mentioned above, signaling information is carried in 51-multiframes.For example, in downlink direction (from BS to MS) in a combination oflogical channels containing the SCH, the SCH is always transmitted inframes number #1, #11, #21, #31, and #41, respectively, i.e. five timesper 51-multiframe. More precisely, the 51-multiframe is applied in thetime slot 0 of the BCCH, or control channel, frequency.

In GSM/EDGE networks, on the SCH, cell identity is transmitted, and asmentioned above it takes place in 5 frames in each 51-frame controlchannel multiframe. As the networks are typically non-synchronized, afull idle frame must be reserved for terminals for SCH data decodingpurposes. A full idle frame is necessary even in a synchronized network,because one's call can take place in the time slot which coincides withtime slot 0 of the target cell. Cell identities must be established inorder to attach signal level measurements to a particular neighbor cell.The cell identity is transmitted as the base station identity code BSIC.The BSIC is an identifier for the BS although the BSIC does not uniquelyidentify a single BS, since it has to be reused several times per PLMNnetwork (public land mobile network). The BSIC serves for identificationand distinction among neighbor cells, even when neighbor cells use thesame BCCH (broadcast control channel) frequency. Since the BSIC isbroadcast from the BS, the mobile terminal does not even need toestablish a connection to the BS in order to retrieve the BSIC. The BSICin turn consists of the network color code NCC identifying the PLMN andthe base station color code BCC (3 bit) used to distinguish among eightdifferent training sequence codes that one BS may use and to distinguishbetween eight neighboring base stations without a need for the mobileterminal to register on any other BS.

On full rate channels (FR), one frame in each 26-frame TCH multiframe isreserved for this purpose of SCH decoding, as seen from FIG. 3.

However, as the relative phases of TCH and control channel multiframesare random, in the worst case on a FR channel, one must attempt SCHdecoding 11 times before it may be performed successful. The duration ofthis process is approximately 1.32 seconds. The reason therefore is thatonly after 286 frames (=11*26 multiframes) there occurs (for the firsttime) a coincidence and/or full overlap in time between a SCH frame in a51-multiframe and an idle frame in a 26-multiframe. Thus, a delay indecoding of 286*4.615 ms=1319.89 ms≈1.32 s is caused.

Thus, as set out above, in GSM/EDGE cellular networks there is a delayin decoding the SCH data from a new neighbor cell. In the worst case itcan be about 11 traffic channel (TCH) multiframes, or 1.32 seconds.

In preparation for a handover, however, one must decode SCH data fromseveral neighbor cells and perform a number of signal level measurementson the neighbors. In cellular networks adopting e.g. a microcell networkarrangement, fast moving mobiles may require frequent inter-cellhandovers due to frequent cell border crossings.

Just as a numeric example, assume a microcell cellular network ofmicrocells having a radius r=500 m. A mobile terminal starting to movefrom approximately the center of a cell would encounter a need forhandover after (radially) traveling a distance of about r=500 m.Assuming further a speed of 100 km/h (=27.7 m/s), the mobile terminalwould reach the microcell border after about 18 seconds. Assumingfurther that 6 neighbor base stations are to be monitored, 6*1.32 s=7.92s were required for decoding/measuring the SCH of the neighbor BS which,being about half the time the mobile terminal needs for traveling, isquite too long for taking a decision concerning handover.

Such delays in neighbor cell SCH decoding and level measurement may thusresult in incomplete data for inter-cell handover decision or evenunsuccessfull handovers.

Previously, a common approach resided in locating fast moving cells inmacrocells. This means that a fast moving mobile terminal was assignedto and handed over to base stations BS serving macrocells only (cellsdenoted with capital letter in FIG. 1).

This, however, is not a feasible solution in networks or areas, whereonly the microcell network layout exists (cells denoted with lowercaseletter in FIG. 1).

SUMMARY OF THE INVENTION

Hence, it is an object of the present invention to solve the abovementioned drawbacks even in a cellular communication network comprisingonly microcells.

According to the present invention, this object is for example achievedby a method of channel allocation for a mobile terminal moving in acellular communication network, said method comprising the steps ofdetecting the speed of said mobile terminal moving in said network, anddependent on said detected speed, allocating a channel of a specifictype to said mobile terminal.

According to advantageous further developments of the present inventionas set out in the dependent claims,

said allocated channel of a specific type is a traffic channel, with thechannel types being distinguishable by their transmission rate,

if said detected speed is below a first speed threshold, a first channelof a specific type is allocated to said mobile terminal,

if said detected speed is above said first speed threshold, anotherchannel of a specific type different from said first channel isallocated to said mobile terminal,

if said detected speed is above said first but below a second speedthreshold, a second channel of a specific type is allocated to saidmobile terminal,

if said detected speed is above said first and above a second speedthreshold, a third channel of a specific type is allocated to saidmobile terminal,

said transmission rate differs by the number of idle frames in amultiframe of a traffic channel,

measurements are conducted on cells neighboring a current cell in whichthe mobile terminal is located, during said idle frames,

the speed of said mobile terminal moving in said network is repeatedlydetected,

said detecting is performed after a predetermined time interval haselapsed,

said cellular communication network is composed of plural cells each ofwhich cell covering a small area such that the coverage area of saidplural small cells may be comprised in the coverage area of a largecell,

said speed threshold is predetermined based on the cell radius of thecells constituting the network and the expected number of handoversoccurring for a mobile terminal moving at a given speed via the cellularnetwork,

allocating a channel of a specific type to said mobile terminal isimplemented based on hysteresis, and

hysteresis is implemented in case that the currently detected speed isdifferent from an immediately preceding detected speed and differs by acertain amount from a speed threshold defined for being used in channelallocation.

Still further, according to the present invention this object is forexample achieved by a device adapted to allocate a channel to a mobileterminal moving in a cellular communication network, said devicecomprising: detecting means adapted to detect the speed of said mobileterminal moving in said network, and control means adapted to allocate achannel of a specific type to said mobile terminal dependent on saiddetected speed.

According to favorable refinements of said device,

said allocated channel of a specific type is a traffic channel, with thechannel types being distinguishable by their transmission rate;

said control means is adapted to allocate a first channel of a specifictype to said mobile terminal, if said detected speed is below a firstspeed threshold;

said control means is adapted to allocate another channel of a specifictype different from said first channel to said mobile terminal, if saiddetected speed is above said first speed threshold;

said control means is adapted to allocate a second channel of a specifictype to said mobile terminal if said detected speed is above said firstbut below a second speed threshold;

said control means is adapted to allocate a third channel of a specifictype to said mobile terminal, if said detected speed is above said firstand above a second speed threshold;

said transmission rate differs by the number of idle frames in amultiframe of a traffic channel;

said detection means is adapted to repeatedly detect the speed of saidmobile terminal moving in said network;

said detection means is adapted to perform said detection after apredetermined time interval has elapsed;

said control means is adapted to perform allocating a channel of aspecific type to said mobile terminal (MS) based on hysteresis;

said control means is adapted to base the allocation on hysteresis incase that the currently detected speed is different from an immediatelypreceding detected speed and differs by a certain amount from a speedthreshold defined for being used in channel allocation;

said control means and said detection means are located at a samenetwork entity;

said control means and said detection means are located remotely fromeach other;

said detection means is located at said mobile terminal to which achannel is to be allocated.

Advantageously, with the present invention implemented, delays inneighbor cell SCH decoding and signal level measurement aresignificantly reduced and may thus no longer result in incomplete datafor inter-cell handover decision or even unsuccessful handovers. Hence,communication network performance in particular in connection withhandovers in a cellular network layouts is improved.

Thus, a continuous call connection even for fast moving mobile terminalsin cellular network layouts (microcell and/or macrocell) due tosuccessful handovers is enabled, while involving only a slight reductionof speech quality on half rate and/or quarter rate transmission channelsassigned to the moving terminals as compared to full rate channels.

Still further, a mobile terminal may perform more frequently signallevel measurements concerning neighbor base stations, i.e. base stationsof cells surrounding the current cell in which the mobile terminal islocated. A rather rapid acquisition of signal level data and SCH datafrom new neighbor cells is enabled by more frequent measurements, whichin turn results in a low delay experienced by a base station controllerBSC receiving measurement data concerning new neighbor cells after aninter-cell handover occurred.

Also, the method of the present invention may easily be implemented tothe control algorithms at the base station controller, while nomodifications to the protocols or the base station subsystem BSS and/orradio access network RAN are required.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood upon referring tothe description of embodiments thereof in combination with the drawings,in which:

FIG. 1 shows a rough outline of a part of a cellular communicationnetwork comprising an overlay of macrocells and microcells,

FIG. 2 illustrates a flowchart for explaining the method according tothe present invention,

FIG. 3 shows a 26-multiframe for a full rate traffic channel,

FIG. 4 shows a 26-multiframe for a half rate traffic channel,

FIG. 5 shows a 26-multiframe for a quarter rate traffic channel,

FIG. 6A shows a characteristic of mapping traffic channel to detectedspeed which is free of hysteresis, and

FIG. 6B shows a characteristic of mapping traffic channel to detectedspeed which is not free of hysteresis.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail with reference tothe accompanying drawings.

As stated above, for a mobile terminal MS moving in a cellularcommunication network NW, channel allocation is performed such that thespeed v of said mobile terminal MS moving in said network is detected,and dependent on said detected speed v a channel of a specific type isallocated to said mobile terminal MS.

This means that in a cellular network, if the speed of the mobileterminal exceeds a specific speed threshold, moving mobile terminals areconsidered to be “fast” moving terminals and are assigned a half rate HRor quarter rate QR speech channel. Thus, the proportion of idle framesas compared to a full rate FR channel is increased. This will greatlyincrease the speed at which synchronization channel SCH data fromneighboring cells (contained in 51-multiframes) can be decoded. This, inturn will reduce the minimum interval between successive inter-cellhandovers. Still further, the idle frames may be exploited to increasethe frequency of neighboring cell level measurements.

FIGS. 3 to 5 show the traffic channel multiframe structure for FR, HRand QR speech channels, respectively. As explained previously, inGSM/EDGE networks cell identity is transmitted on the SCH, and it takesplace in 5 frames in each 51-frame control channel multiframe. As thenetworks are typically non-synchronized, a full idle frame must bereserved for terminals for SCH data decoding purposes. As said above,the full idle frame is also required in synchronized networks. Cellidentities must be established in order to attach signal levelmeasurements to a particular neighbor cell. On FR traffic channels, oneframe in each 26-frame TCH multiframe is reserved for this purpose, asseen from FIG. 3.

The relative phases of TCH multiframes (26-multiframes) and controlchannel multiframes (51-multiframes) are random. Therefore in the worstcase on a FR channel, one must attempt SCH decoding 11 times, before itis successful. The duration of this process is approximately 1.32seconds, as previously explained.

However, on HR traffic channels (TCH), each TCH multiframe contains 13idle frames, as seen in FIG. 4, while on QR channels, the number of idleframes per TCH multiframe is 19, as shown in FIG. 5.

If all 13 idle frames of a HR channel are used for SCH decoding, themaximum number of frames before success is 34. The respective durationis about 156.9 milliseconds. This can be explained as follows. Assume a51-multiframe to be displaced in time versus a 26-multiframe by 12frames, so that frame #0 of the 51-multiframe coincides in time withframe #12 of a 26-multiframe. Then in frame #1 of the 51-multiframe SCHinformation is transmitted, while it may not be decoded at the mobileterminal in the 26-multiframe, since frame #13 of the HR 26-multiframeis a data frame and not an idle frame. The SCH data in the 51-multiframeare transmitted in frames #1, #11, #21, #31, and #41, as mentionedabove. Hence, the first coincidence of an SCH frame in the 51-multiframeand an idle frame of the half rate traffic channel (HR TCH)26-multiframe occurs but for frame #21 of the 51-multiframe whichcoincides (taking into account the above assumed worst case shift) withframe #7 of a second of consecutive 26-multiframes. Apparently, withreference to frame #0 of the first 26-multiframe, SCH decoding occursfor the first time after 34 frames (26 frames of the 1^(st)26-multiframe+8 frames of the 2^(nd) 26-multiframe), corresponding to adelay of 34*4.615 ms/frame=156.9 ms.

Correspondingly, if all 19 idle frames of a QR channel are used for SCHdecoding, the maximum required number of frames is 11. This equals adelay of about 51 milliseconds (11*4.615 ms/frame=50.8 ms). Thissituation occurs upon a 51-multiframe being shifted by one frame withregard to the 26-multiframe so that frame #1 of the 51-multiframecoincides with frame #0 of the 26-multiframe. Then, a first SCH decodingis possible in frame #10 of the 26-multiframe being an idle frame in theQR channel.

Apparently, when switching, dependent on the terminal's speed, from afull rate to a half rate and/or quarter rate channel, SCH frame decodingat the mobile terminal side will be greatly accelerated as compared tothe case of a full rate channel.

Still further, a reliable inter-cell handover decision requires a numberof signal level measurements from each candidate target cell(surrounding/neighbor cells to a current cell in which the mobileterminal is located). In addition to receiving and sending data, currenthalf-duplex terminals are capable of measuring one neighbor cell in eachframe. (Half duplex describes communications in a single direction at atime, i.e. one side sends and the other side receives. When the rolesreverse, the sending side now receives and the receiving side nowsends.) During an idle frame, it would however be possible to performthe respective measurement of three or four neighbor cells. This willalso expedite the preparation for inter-cell handovers, which isbeneficial for fast moving mobiles in cellular networks.

As regards the determination and/or detection of the mobile terminalspeed, several methods are known on a link level as well as on a networklevel, which are considered not be necessarily to be described here.

FIG. 2 illustrates a flowchart for explaining the method according tothe present invention. The method of channel allocation for a mobileterminal moving in a cellular communication network starts in step S20.

Then, the process proceeds to step S21.

In step S21, the mobile terminal's speed is detected. This can be doneat the mobile terminal's side according to commonly known principles.Nevertheless, the speed detection may as well, or rather more likely, beeffected by the network.

Upon detection of the mobile terminal speed, in step S22 a timer isinitialized and started. The timer may be any means suitable to monitorthe lapse of time after a speed detection.

Subsequently, in step S23, a judgement is made as to whether thedetected speed exceeds a first speed threshold. A speed threshold is setin order to judge whether the mobile terminal moves slow and/or not fast(if the detected speed is below the threshold) or moves fast (if thedetected speed is above the threshold). The speed threshold may bepredetermined and fixed for the mobile terminal. Nevertheless, it mayalso be variable and be determined according to the need. For example,dependent on the size of a cell e.g. microcell/macrocell, differentspeed thresholds could be used to judge whether a terminal is movingfast or slow. For example only, in a microcell of 500 m radius, a speedof >50 km/h could already be regarded as being fast and requiringfrequent handovers, while in a microcell of 2000 m radius, only a speedof >100 km/h could be regarded as being fast and requiring frequenthandovers.

As the cell radius is to some extent also dependent on the transmitpower of the base stations, the speed threshold could therefore bedefined dependent on the BS transmit power levels. In areas where smallcells (microcells) are deployed, the networks are typically interferencelimited and not coverage limited. Hence a cell area is riot determinedsolely by the base station output power, but by “dominance”. Stated inother words, the area of a particular cell equals that geographicalarea, in which the respective base station is received stronger (better)than the base stations of the surrounding cells. Therefore, base stationtransmit power level is not an optimum measure for setting the speedthresholds, but could for example only, more conveniently be combinedwith interference measurement data, or the like. Furthermore, forexample, an improved manner for setting the speed threshold is to usesimply the size (or more precisely, the dominance area) of a cell. Thecell size is used to set the speed thresholds which are then used inthis cell for determining the proper channel to be used. Since cell sizeand dominance are topics that are planned during network planning alsothe speed thresholds can be planned in advance in a similar way.

Such modifications, however, are not shown in the drawing and thesubsequent description will assume a fixed speed threshold in order tokeep the explanation simple.

Note that as the network totally controls the handover (and it knows thetype of cell, cell radius etc.) it can autonomously decide the strategyit applies to a respective mobile terminal.

Thus, if NO in step S23, and the mobile terminal is judged to be notfast, a “normal” full rate channel is allocated for base station mobileterminal communication, see step S24.

However, if in step S23 a decision is taken in terms of the terminalbeing judged as a fast moving terminal (YES in step S23), the flowadvances to step S25. Step S25 is similar to step S23 with the onlydifference that a second speed threshold is judged in terms of beingexceeded or not by the detected speed. Also the second threshold couldbe fixed or variable as explained in connection with the firstthreshold. Also, for the purpose of the present invention, a singlespeed threshold is already sufficient and a second threshold isoptional. Nevertheless, the more different specific channel types thereare to be assigned, the more preferable it is to use plural thresholdsto more properly judge which of these channels is to be allocated.

Thus, if NO in step S25, a half rate channel HR is allocated (step S26)since the terminal although considered in step S23 as being “fast” isnot significantly faster. On the other hand, if YES in step S25, aquarter rate channel QR is allocated (step S27), since the terminal isnot only considered to be fast but to be “significantly” faster since itexceeds the second threshold.

After steps S24, S26 and S27, the flow is combined in step S28. In stepS28 the expiry of the timer started in step S22 is checked. If the timerhas not expired (NO in step S28), the flow returns and loops throughstep S28 until the timer expires.

If the timer expires, the flow returns from step S28 to step S21 wherethe terminal speed is detected again and the process is repeated fromstep S21 onwards. The time period monitored may be fixedly determined ormay be variable. The time period may be set according to an expectedbehavior of the subscriber using the mobile terminal or the like. Also,it may be set according to the previous behavior of the user derivablefrom a number of the past speed measurements for the terminal whichcould be recorded.

Note that FIG. 2 only shows an example according to which only FR, HRand QR channels are allocated dependent on the detected speed.Nevertheless, it is of course conceivable to adapt the method flowchart(not shown) such that in case of YES in step S25, another (third) speedthreshold is judged (not shown) and as a result of not exceeding orexceeding the third threshold, either the QR channel is allocated (NO)or e.g. the QR channel is allocated while being switched to a DTX mode(YES). Alternatively, in such a latter case of “YES”, it could also beconceivable that the network refuses to allocate a channel to the mobileterminal. (Still further, a forced handover e.g. to a macrocell overlaidto the current (microcell) could be performed, if such amicro-/macrocell overlaiy network layout is present.)

Also, irrespective of a third speed threshold being exceeded or not, itis of course possible that DTX mode can be used in order to enhance SCHdecoding speed and level measurement frequency on any channel, i.e. FR,HR, and/or QR channels.

According to the present invention, a channel to be used is determinedby mapping the channel type to the detected speed of the terminal. Everytime, the detected speed exceeds a threshold or does not exceed thethreshold, the corresponding channel is allocated for transmission. Thissituation (and as described before) is illustrated in FIG. 6A showing acharacteristic of mapping traffic channel to detected speed. Thischaracteristic is free of hysteresis.

In case speed is detected to have increased as compared to a previousspeed detection, a rather immediate channel change is beneficial in thatthe handover information may readily and early enough be acquired asexplained above, so that handover failures are widely avoided.

However, in case a detected speed is smaller than a previously detectedspeed it could be advantageous not to immediately change the channeltype, since the speed might rise again shortly afterwards. Dependent onthe time interval for speed detection this might lead to an oscillatingbehavior in channel allocation, which is mostly undesired from a networkresource management point of view. Therefore, in such a case, acharacteristic involving some hysteresis in case a speed is detected tohave fallen below a threshold value is beneficial. For example, amotivation for providing hysteresis is that in addition to user behavior(e.g. stopping at traffic lights indicating “red”) inaccuracies in speedestimation cause a need for hysteresis.

Such a characteristic is shown in FIG. 6B. That is, only if a detectedspeed is a certain amount (Δ1, Δ2SONDZEICHEN) below a threshold (1^(st),2^(nd) threshold, respectively), a channel allocated is changed.Otherwise, the allocated channel is still maintained. In order toimplement such a characteristic, a knowledge of the previous, i.e.preceding speed has to be present in the system, and a further thresholdhas to be checked (e.g. 1^(st) threshold minus delta_1, as shown in FIG.6B) for each of the 1^(st) to 2^(nd) speed thresholds.

Nevertheless, hysteresis may alternatively or additionally be alsoapplied in upward direction (not shown in FIG. 6B). That is, only if adetected speed is a certain amount (e.g. delta_1 above a threshold(1^(st), 2^(nd) threshold, respectively), a channel allocated ischanged. Otherwise, the allocated channel is still maintained. In orderto implement such a characteristic, a knowledge of the previous, i.e.preceding speed has to be present in the system, and a further thresholdhas to be checked (e.g. 1^(st) threshold plus delta_1, similarly to thesituation shown in FIG. 6B) for each of the 1^(st) to 2^(nd) speedthresholds.

Stated in more general words, hysteresis can be implemented such thatanother channel is allocated in case that the currently detected speedis different from an immediately preceding detected speed and differs bya certain amount from a speed threshold defined for being used inchannel allocation.

Although herein before a particular focus has been laid on thedescription of the method according to the present invention, it is tobe understood that the present invention of course also concerns anaccordingly adapted device adapted to allocate a channel to a mobileterminal moving in a cellular communication network. In particular, thedevice according to the present invention which is adapted to implementthe method according to the present invention comprises detecting meansadapted to detect the speed of said mobile terminal moving in saidnetwork, and control means adapted to allocate a channel of a specifictype to said mobile terminal dependent on said detected speed.

According to further aspects concerning said device, said allocatedchannel of a specific type is a traffic channel TCH, with the channeltypes being distinguishable by their transmission rate FR, HR, QR; saidcontrol means is adapted to allocate a first channel of a specific typeFR to said mobile terminal MS, if said detected speed is below a firstspeed threshold; said control means is adapted to allocate anotherchannel of a specific type HR, QR different from said first channel tosaid mobile terminal, if said detected speed is above said first speedthreshold S23; said control means is adapted to allocate a secondchannel of a specific type HR to said mobile terminal if said detectedspeed is above said first but below a second speed threshold S26; saidcontrol means is adapted to allocate a third channel of a specific typeQR to said mobile terminal, if said detected speed is above said firstand above a second speed threshold S27; said transmission rate FR, HR,QR differs by the number of idle frames in a multiframe of a trafficchannel; said detection means is adapted to repeatedly S28, S21 detectthe speed of said mobile terminal MS moving in said network; saiddetection means is adapted to perform said detection S21 after apredetermined time interval has elapsed S28; said control means isadapted to perform allocating S24, S26, S27 a channel of a specific typeto said mobile terminal MS based on hysteresis; said control means isadapted to base the allocation on hysteresis in case that the currentlydetected speed is different from an immediately preceding detected speedand differs by a certain amount from a speed threshold defined for beingused in channel allocation; said control means and said detection meansare located at a same network entity; said control means and saiddetection means are located remotely from each other; said detectionmeans is located at said mobile terminal to which a channel is to beallocated.

As set out above, the present invention proposes a method of channelallocation for a mobile terminal MS moving in a cellular communicationnetwork NW, said method comprising the steps of: detecting S21 the speedof said mobile terminal MS moving in said network, and dependent on saiddetected speed S23, S25, allocating S24, S26, S27 a channel of aspecific type to said mobile terminal MS. Accordingly, with the presentinvention implemented, delays in neighbor cell SCH decoding and signallevel measurement are significantly reduced and may thus no longerresult in incomplete data for inter-cell handover decision or evenunsuccessfull handovers. Hence, communication network performance inparticular in connection with handovers in a cellular network layout isimproved. The present invention also concerns an accordingly adapteddevice for channel allocation.

Although the present invention has been described herein above withreference to its preferred embodiments, it should be understood thatnumerous modifications may be made thereto without departing from thespirit and scope of the invention. It is intended that all suchmodifications fall within the scope of the appended claims.

1. A method of channel allocation for a mobile terminal moving in acellular communication network, said method comprising the steps of:detecting a speed of said mobile terminal moving in said network; anddependent on said detected speed, allocating a channel of a specifictype to said mobile terminal, wherein if said detected speed is below afirst speed threshold, a first channel of a specific type is allocatedto said mobile terminal, and said first speed threshold is predeterminedbased on a cell radius of cells constituting the network and an expectednumber of handovers occurring for the mobile terminal moving at a givenspeed via the network.
 2. A method according to claim 1, wherein saidallocated channel of a specific type is a traffic channel, with thechannel types being distinguishable by their transmission rate.
 3. Amethod according to claim 2, wherein said transmission rate differs bythe number of idle frames in a multiframe of a traffic channel.
 4. Amethod according to claim 3, further comprising a step of conductingmeasurements on cells neighboring a current cell in which the mobileterminal is located, during said idle frames.
 5. A method according toclaim 1, wherein if said detected speed is above said first speedthreshold, another channel of a specific type different from said firstchannel is allocated to said mobile terminal.
 6. A method according toclaim 5, wherein if said detected speed is above said first but below asecond speed threshold, a second channel of a specific type is allocatedto said mobile terminal.
 7. A method according to claim 5, wherein ifsaid detected speed is above said first and above a second speedthreshold, a third channel of a specific type is allocated to saidmobile terminal.
 8. A method according to claim 1, wherein the speed ofsaid mobile terminal moving in said network is repeatedly detected.
 9. Amethod according to claim 8, wherein said detecting is performed after apredetermined time interval has elapsed.
 10. A method according to claim1, wherein said cellular communication network is composed of pluralcells each of which cell covering a small area such that the coveragearea of said plural small cells may be comprised in the coverage area ofa large cell.
 11. A method according to claim 1, wherein allocating achannel of a specific type to said mobile terminal is implemented basedon hysteresis.
 12. A method according to claim 11, wherein hysteresis isimplemented in case that the currently detected speed is different froman immediately preceding detected speed and differs by a certain amountfrom a speed threshold defined for being used in channel allocation. 13.A device adapted to allocate a channel to a mobile terminal moving in acellular communication network, said device comprising: detecting meansadapted to detect a speed of said mobile terminal moving in saidnetwork; and control means adapted to allocate a channel of a specifictype to said mobile terminal dependent on said detected speed, whereinsaid control means is adapted to allocate a first channel of a specifictype to said mobile terminal, if said detected speed is below a firstspeed threshold, and said first speed threshold is predetermined basedon a cell radius of cells constituting the network and an expectednumber of handovers occurring for the mobile terminal moving at a givenspeed via the network.
 14. A device according to claim 13, wherein saidallocated channel of a specific type is a traffic channel, with thechannel types being distinguishable by their transmission rate.
 15. Adevice according to claim 14, wherein said transmission rate differs bythe number of idle frames in a multiframe of a traffic channel.
 16. Adevice according to claim 15, wherein said control means is adapted toallocate another channel of a specific type different from said firstchannel to said mobile terminal, if said detected speed is above saidfirst speed threshold.
 17. A device according to claim 16, wherein saidcontrol means is adapted to allocate a second channel of a specific typeto said mobile terminal if said detected speed is above said first butbelow a second speed threshold.
 18. A device according to claim 16,wherein said control means is adapted to allocate a third channel of aspecific type to said mobile terminal, if said detected speed is abovesaid first and above a second speed threshold.
 19. A device according toclaim 13, wherein said detection means is adapted to repeatedly detectthe speed of said mobile terminal moving in said network.
 20. A deviceaccording to claim 19, wherein said detection means is adapted toperform said detection after a predetermined time interval has elapsed.21. A device according to claim 13, wherein said control means isadapted to perform allocating a channel of a specific type to saidmobile terminal based on hysteresis.
 22. A device according to claim 21,wherein said control means is adapted to base the allocation onhysteresis in case that the currently detected speed is different froman immediately preceding detected speed and differs by a certain amountfrom a speed threshold defined for being used in channel allocation. 23.A device according to claim 13, wherein said control means and saiddetection means are located at a same network entity.
 24. A deviceaccording to claim 13, wherein said control means and said detectionmeans are located remotely from each other.
 25. A device according toclaim 24, wherein said detection means is located at said mobileterminal to which a channel is to be allocated.